Actually, there are. But those positions are few and far between. Generally only large scale companies who make AAA RPG titles hire full-time staff writers. Bioware is the one that comes to mind. They are hiring writers for both offices. Other than that the only way you will find a job just as a writer is through freelance, and that's a huge endeavor to undertake.

If you want to write for games and can't get hired by a company that employs staff writers (or don't want to deal with freelancing) then your best bet is learning the ins and outs of game design. The harsh reality is that most companies don't hire game designers at entry level, but there are more Junior Designer positions open than there are Writer positions, heh. So learn about gameplay design, systems design, and level design. Then join a mod team and get experience as a designer. Ask to work on writing tasks. Present your experience to an employer. Once you're in, demonstrate your writing skills and tell your boss that you feel your talents lie in writing. Ideally you will be given more tasks that involve writing, which is on par with a designer since most studios just have their designers act as writers.

Sadly the industry still functions under the thought that "anyone can write". Writers are just now beginning to gain recognition as a valuable part of a core game development team, but it's still going to take a long time before we see more studios willing to hire writers to work on staff year-round. Until then, learn -something-. Design will aid you best, but the important part is that you just get into the industry. Then show them how you can really shine.